Topic 2 - Grapevine vegetative cycle and dormancy

Question 1

What are the main vegetative organs?

Answer 1

• shoots
• leaves
• arm
• trunk
• root system

Question 2

What is bleeding?

Answer 2

• Xylem sap flowing out from non-suberised wound surface
• Late autumn or early spring
• Rehydrate xylem and buds
• Prepared for budburst

Question 3

What induces bleeding?

Answer 3

• Remobilisation of root reserves (sugars, acids, and amino acids)

Question 4

What factors effect budburst?

Answer 4

Temperature:
- Chilling requirement: low for V. vinifera
- Average maximum and minimum temperature 10 days before budburst
- Air and soil temperature.

Pruning:
- Delay pruning: postponing budburst.
Cool climate (early) and frost-prone regions (late).

Variety:
- Early and late budburst varieties
- Rootstock-scion interaction.

Question 5

What is apical dominance?

Why is it not favourable?

What is is a method to manage apical dominance?

Answer 5

Apical buds burst first and suppress the burst of more proximal buds.

It may relate to the production of Auxin which accumulates at the proximal end of the cane suppressing budburst.

It is not favourable because it can cause erratic budburst.

A method to manage apical dominance is to bend the cane into an arch shape when we do winter pruning.

Question 6

What is fixed growth?

Question 7

What is free growth?

Answer 7

• Generally produces smaller leaves and shorter internodes.

Question 8

Is the shoot growth rate consistent throughout the season? Describe the growth rate.

Answer 8

No. It is:
- Slow after budburst
- Positively linearly related to heat degree days reaching maximum around or soon after flower
- Decrearses after flowering and ceases after veraison.
- At veraison each shoot has an average of 30-35 nodes and the shoot begins to lignify from the proximal to distal end.

Question 9

What is vigour?

Answer 9

The rate of shoot growth or the shoot elongation overtime is referred to as vigour.

Question 10

What factors impact shoot growth?

Answer 10

• Climate and environment
• Cultural practice
• Variety

Question 11

Why is it better to prune after leaf fall (senescence)?

Answer 11

Some nutrients from the leaves are recycled back to the vine before leaf fall.

Question 12

What are the two types of secondary growth in the trunk and arms of a grape vine?

Answer 12

1. Cork cambium:
   - Inside: Phelloderm cells
   Outside: Cork cells
2. Vascular cambium:
   - Inside: Secondary xylem
   - Outside: Secondary phloem

Question 13

Describe the growth patterns of grapevine roots.

Answer 13

Growthoots keep accumulating biomass throughout the growing season.

Follows diurnal pattern meaning the rate is higher in the afternoon than night because the temperature in the soil is higher in the afternoon.

Within the growing season there are 1-2 flushes of root growth. Roots begin to grow around budburst and peaks around flowering. If there’s a second growth it occur after Veraison and continues to harvest.

Question 14

What are prompt buds?

What are latent buds?

Answer 14

Prompt buds:

• Remain dormant or burst in the current season (lateral shoots)
• Generally not fruitful.

Latent buds:

• Remain dormant: overwinter buds and burst next spring.
• Also called compound bud containing 3 seperate buds: 1 primary + 2 accessory

Question 15

What are the three phases of dormancy?

Answer 15

1. Conditional (or pre-dormancy or paradormancy)
   - buds have potential to burst, but not: chemical or physical conditions
   Conditions removed and buds will burst
   Apical dorminance
2. Organic (dormance or endodormancy)
   - buds can not burst under ideal conditions
   - Shorten day-length / main shoot growth ceased, lasts 2-3 months
   - Buds at proximal end enter dormancy first before apical buds.
3. Enforced (post-dormancy, or ecodormancy)
   - Ready to burst
   - Waiting for the right environmental conditions (e.g., chilling requirement and proper ambient and soil temperatures)

Question 16

What is the difference between vegetative and reproductive growth?

Answer 16

Vegetative growth includes growth of the shoot, trunk, arms and roots, while reproductive growth comprises inflorescence induction, initiation and formation, flowering and fruitset, berry formation and berry ripening.

Question 17

How long does it take for most of the observed renewable tissues on a grapevine to form?

Answer 17

Most of the observed renewable tissues on the grapevine require two years to form, i.e., the first year as compound buds, and the second year as emerged shoots.

Question 18

What is grapevine phenology? What does it help guide?

Answer 18

• Phenology studies the annual sequence of plant development. In viticulture, phenology is focused on the timing of specific stages of growth and development in the annual cycle.
• Can help site and cultivar selection, vineyard design, planning of labour and equipment requirements, and timing of cultural practices.

Question 19

What are the main distinct developmental stages identified for grapevines?

Answer 19

• Dormancy, budburst, flowering, fruitset, veraison, harvest, leaf senescence and leaf fall.

Question 20

How long can bleeding last?

Answer 20

It can last for few days to several weeks, or follow a ‘stop-and-go’ process.

Question 21

What causes bleeding?

What factors impact bleeding?

Answer 21

Bleeding is caused by root pressure, which is induced by the remobilisation of nutrients stored in the permanent woody root structure.

Therefore, factors influencing root metabolism, such as soil temperature, soil moisture, and also the type of rootstock itself, all impact bleeding.

Generally, soil temperature above approximately 7 °C can initiate bleeding. When the soil is too dry, bleeding can be minimal or even absent.

Question 22

How can soil temperature impact bleeding?

Answer 22

Generally, soil temperature above approximately 7 °C can initiate bleeding.

When the soil is too dry, bleeding can be minimal or even absent.

Question 23

How does the remobilisation of nutrients in roots cause bleeding?

Answer 23

The remobilisation of the nutrients increases the concentration of sugars, organic acids, and amino acids in the xylem sap, which drives the uptake of water by roots from the soil.

Question 24

What is a chilling requirement?

Answer 24

• The buds of woody perennial plants generally have a chilling requirement to burst.
• Compared to other woody perennial plants, whose buds will not burst unless experiencing a period of chilling, Vitis vinifera seems to have a very low chilling requirement.
• Cold conditions in late autumn to early winter is satisfiable.

Question 25

How does temperature effect budburst?

Answer 25

- Earlier budburst can be expected if higher than average maximum temperature in the month prior to budburst has been reached, regardless of the whole vines or individual buds are exposed to the heat. - soil temperature in the rootzone also positively correlated with budburst date. Therefore, well-drained, stony or calcareous soil can lead to earlier budburst than wet and clay soil, which is preferred in cool climate regions to achieve a longer growing season.

Question 26

How may the timing of winter pruning affect the time of budburst? How can this be put into practice?

Answer 26

Delaying or advancing pruning can induce later or earlier budburst, respectively. - Earlier pruning could be implemented in cool climate regions to achieve prolonged growing season. - In frost- and/or hail-prone regions, spur pruning the grapevines in spring, just after the buds on the ends of the canes have burst, can significantly delay the burst of the retained buds.

Question 27

Why is the variety and rootstock and important factor in budburst?

Answer 27

- The order of budburst of different varieties tends to be maintained regardless of any environmental factors. - Early-bursting varieties do not need temperatures as high as the late-bursting varieties, so they fit frost-prone locations better.

Question 28

What is auxin and how does the impact vine growth?

Answer 28

- The production of auxin within the apical growing tip is generally regarded as the main reason for apical dominance. - A high concentration of auxin is produced from the growing bud and transported downward along the cane or spur, so that the burst and growth the rest of the attached buds are suppressed.

Question 29

What occurs when all preformed fixed nodes have fully expanded?

Answer 29

- The shoot apical meristem continues to divide and to produce new nodes, i.e., free nodes, under favourable growing conditions, until the cessation of the shoot growth. - Compared to fixed nodes, these free nodes generally generate smaller leaves and shorter internodes.

Question 30

What is shoot elongation postively linearly related to after budburst and before flowering?

Answer 30

Shoot elongation is positively linearly related to Heat Degree Days (HDD) within this period.

Question 31

What are prompt buds?

Answer 31

- The only true axillary buds of the main shoot, give rise to lateral buds. - Mostly break in the current season (i.e., lateral shoots). - Generally not fruitful. But if produced, it is called second crop. Pinot noir tends to produce second crop.

Question 32

What are latent buds?

Answer 32

- Located between the prompt bud (i.e., lateral shoot if bursts) and the main shoot. So they are technically the secondary lateral buds, and formed later than the prompt buds. - Remain dormant overwinter, which burst during next spring, or hidden for years, which grow into watershoots or other permanent structure. - A 'compound bud' can contain multiple latent buds, i.e., one primary bud and one to two accessory buds.

Question 33

What may occur if there are an excessive number of lateral shoots? What can be done to manage this?

Answer 33

They make up a very dense canopy, and cause problems such as reduced photosynthesis capacity and the quality and quantity of the fruits, and increased energy consumption by respiration and disease incidences. In this case, lateral shoot removal can be implemented as a canopy management technique to open up the canopy. Avoid trimming to suppress the growth of the lateral shoots.

Question 34

How does air and root temperature regulate shoot growth?

Answer 34

- Both air and root temperature positively regulate shoot growth, i.e., the higher the temperature, the higher the growth rate under controlled conditions. - Cool to moderate climate favours shoot vigour, and therefore better internode elongation and stem thickness can be achieved.

Question 35

How does water stress affect shoot vigour and leaf area?

Answer 35

Water stress induces reduced shoot vigour and leaf area. The sensitivity of internode elongation, node/internode formation, and tendril growth to water stress is high, low, and high, respectively.

Question 36

How does light and wind intensity affect shoot elongation, node numbers, and shoot width?

Answer 36

Light intensity has little effect on shoot elongation or node number, but low light leads to thinner shoots. Wind can alter shoot morphology and significantly reduce shoot growth.

Question 37

How does vine density relate to shoot growth?

Answer 37

Higher vine density leads to decreased shoot growth, but not necessarily impacts leaf area per hectare.

Question 38

How does pruning and shoot thinning affect growth?

Answer 38

Minimal pruning produces higher leaf area per vine than cane pruning. Shoot thinning can stimulate the growth of the remaining shoots, especially if carried out in early season.

Question 39

How does shoot position and positioning affect growth?

Answer 39

Vertical position favours shoot vigour. Compared to horizontal shoots, positioning shoots vertically upright can accentuate shoot vigour, while downwards shoots have reduced vigour.

Question 40

How does variety affect shoot vigour? What are some examples?

Answer 40

Shoot vigour is also a genotype of different grapevine varieties. For example, Shiraz has greater vigour than Cabernet Sauvignon, and Merlot is more vigorous than Cinsaut.

Question 41

What are the factors influencing grapevine leaf development?

Answer 41

- Light - Water - Vigour and vine age

Question 42

How does light influence grapevine leaves development?

Answer 42

Shading leads to thinner leaves with smaller palisade parenchyma cells and less spongy parenchyma cells.

Question 43

How does water influence grapevine leaves development?

Answer 43

Water stress leads to smaller epidermal cells and lower nitrogen concentration. Prolonged water stress causes smaller but more leathery leaves.

Question 44

How does vigour and vine age influence grapevine leaves development?

Answer 44

Vigorous shoots generally produce longer internodes, larger leaves, and well-developed lateral shoots, and eventually achieve a dense canopy. Vine age generally has a minor effect on grapevine leaves, but shoot vigour tends to decline as vine ages.

Question 45

What happens to grapevine shoots around veraison?

Answer 45

- Around veraison, grapevine shoots begin to lignify. - The colour of the shoots turns from green to brown, and the textures becomes woody, moving from the proximal to the distal. - From then on, a shoot converts to a cane.

Question 46

What is the purpose of lignification?

Answer 46

Lignification can protect vascular tissues and cambiums during winter.

Question 47

What triggers leaf senescence?

Answer 47

The commencement of leaf senescence is triggered by decreasing day length. Lower or extreme high temperature can only accelerate such process.

Question 48

Why does the biomass of the trunk, arms, and roots decrease from midwinter to flowering?

Answer 48

To support the early growth of the shoots and leaves, the biomass of the trunk, arms and roots decreases from midwinter to flowering.

Question 49

What causes the growth of trunk and arms?

Answer 49

The growth of trunk and arms is caused by the renewed activity of cambium and phellogen each season. Cambial activity leads to new xylem formation on the inside and new phloem on the outside. The renewal of xylem each year forms the distinctive annual ring.

Question 50

Why do grapevine roots follow a diurnal pattern?

Answer 50

Within one day, the growth rate tends to relate to soil temperature, so that higher growth rate is observed in the afternoon, and it slows down at night.

Question 51

Why do grapevine roots follow a seasonal pattern?

Answer 51

From a seasonal perspective, the major root growth corresponds to the overall photosynthesis capacity of the whole vine, that carbohydrate availability plays as the driving force.

Question 52

What are the factors affecting root growth?

Answer 52

- Soil character - Mechanical resistance - Soil aeration - Soil temperature - Nutrient supply - Irrigation and soil water status - Rootstock - Planting density - Trellis type - Soil management - Pruning method

Question 53

Describe how soil character affects root growth. What is ideal rooting depth for optimised root growth?

Answer 53

Soil strength, compaction, and the existence of impervious layers can limit rooting depth. For optimised root growth, rooting depth of 70 cm should be reached for irrigated vineyards, and 100 cm for unirrigated vineyards.

Question 54

Describe how soil aeration affects root growth.

Answer 54

Grapevines are very sensitive to waterlogging. The critical air-filled porosity is about 10% by volume.

Question 55

Describe how soil temperature affects root growth.

Answer 55

Without other limiting factors, root growth is closely related to soil temperature. A minimal of 6 °C is required, and the optimal temperature is around 30 °C.

Question 56

What nutrients are important for root growth?

Answer 56

Calcium and boron are important for root growth. Nitrogen and phosphorus improve root branching.

Question 57

How does rootstock affect root density?

Answer 57

Rootstocks with Vitis rupestris parentage typically have deeper roots, while Vitis riparia tends to form shallower and more branched roots.

Question 58

What is the relationship between planting density and root growth?

Answer 58

The higher the planting density, the less root system per vine, but the higher density per unit soil volume. High planting density generally leads to deeper roots.

Question 59

What is the relationship between trellis type and the root structure?

Answer 59

The grapevine always balances the size of the roots and its above ground structure. So larger trellis generally leads to higher root density.

Question 60

What does tillage or permanent swards do to root density in surface soil? What does mulching do?

Answer 60

Tillage or permanent swards generally decrease root density in surface soil, while mulching increase root density.

Question 61

How does winter pruning affect root growth?

Answer 61

Winter pruning tends to stimulate root growth, but more research is still required in this area of viticulture.

Question 62

What are buds?

Answer 62

Young, compressed shoots, whose internodes have not yet elongated and are enclosed in scales or bracts.

Question 63

Where are all buds formed?

Answer 63

All buds are formed by the shoot apical meristem.

Question 64

What is a bract and how does it relate to a bud?

Answer 64

- The sign of bud formation is the initiation of bracts, which turn to brown colour during dormancy. - Bracts protect the bud against desiccation and freezing. - Within the bracts, there are long, woolly epidermal hairs that cushions the bud.

Question 65

What is a prompt bud?

Answer 65

As the shoots from current season are growing, buds for next year start to develop. The first bud to form in the leaf axil is a prompt bud, also called lateral bud, which generally bursts soon after its formation to give lateral shoot.

Question 66

What is a latent bud?

Answer 66

A secondary bud, named as latent bud, is formed by lateral bud (i.e., prompt bud) apical meristem at the location next to the lateral bud and main shoot (i.e., the lateral shoot axil), but at slower developing rate compared to the lateral bud.

Question 67

What is primary bud necrosis (PBN)? What are factors contributing to PBN? What does PBN cause?

Answer 67

- a physiological disorder leading to the death of the primary bud - high shoot vigour, water stress, shading, excess plant growth regulators, low levels of bud carbohydrates and rootstocks have been identified as factors contributing to PBN. - PBN usually causes reduced bud fruitfulness.

Question 67

How is dormancy defined? What does dormancy achieve?

Answer 67

Dormancy is defined as ‘any temporary growth suspension of a plant structure containing a meristem’. It prepares the buds to survive through the wintertime, and lasts from the early summer of the first season to the spring of the second season.

Question 68

What is cold hardiness? How is it achieved?

Answer 68

Cold hardiness is the ability of the bud to bear very cold temperature conditions, typically in the order of -10 to -20 °C. To adapt to the low temperature, buds reduce water content from 80% to 50%, lower respiration rate, and accumulate cryoprotectants to avoid freezing damage caused by water.

Question 69

What is long-term bud dormancy? What is an example?

Answer 69

- Grapevines can remain dormant for long periods of time without loss of viability. - Watershoots on the trunk and cordons are examples.

Question 70

Under the context of climate change, what would happen to grapevine phenology?

Question 71

What cultural operations could be done to minimise any potential negative influences of apical dominance?

Question 72

Why grapevine establishes current growth pattern of shoots and roots?

Question 73

Summarise the benefits of bud dormancy.